JavaScript® Bible, Sixth Edition

Chapter 43. Data-Entry Validation

IN THIS CHAPTER

• Validating data as it is being entered

• Validating data immediately prior to submission

• Organizing complex data-validation tasks

Give users a field in which to enter data and you can be sure that some users will enter the wrong kind of data. Often the mistake is accidental—a slip of the pinkie on the keyboard; other times, users intentionally type the incorrect entry to test the robustness of your application. Whether you solicit a user's entry for client-side scripting purposes or for input into a server-based CGI or database, you should use JavaScript on the client to handle validation of the user's entry. Even for a form connected to a server application, it's far more efficient (from the perspective of bandwidth, server load, and execution speed) to let client-side JavaScript get the data straight before your server program deals with it.

Real-Time versus Batch Validation

You have two opportunities to perform data-entry validation in a form: as the user enters data into a form and just before the form is submitted. I recommend you take advantage of both of these opportunities.

Real-time validation triggers

The most convenient time to catch an error is immediately after the user makes it—especially for a long form that requests a wide variety of information. You can make the user's experience less frustrating if you catch an entry mistake just after the user enters the information: his or her attention is already focused on the nature ...